It is the purpose of this proposed study to test the hypothesis that younger sisters of teenaged mothers constitute an identifiable population at higher risk of becoming pregnant themselves before the age of 20. Using two secondary data sources from the Arkansas Department of Social Services, we propose to test this hypothesis with an historical-prospective (cohort) strategy. Two types of families eligible for Medicaid will be studied, both of which have at least two daughters in the susceptible age range during the study period (1976-1978). The first family type (P) will be one in which an older sister was pregnant in 1976; the second group of families (O) will consist of those in which none of the sisters was pregnant in 1976. Younger sisters in both P-type and O-type families will be followed through record linkage, from 1977-1978, to determine the number and timing of their pregnancies. It is hypothesized that those younger sisters in P-type families will experience significantly higher rates of pregnancy and at significantly younger ages than will those in O-type families when control is made for other risk factors. If this hypothesis is upheld by the results of this study, there will be strong evidence to suggest that younger sisters of pregnant teens comprise an unusually vulnerable risk group for experiencing a teen pregnancy themselves. This finding could have important programmatic applications for primary prevention of teen pregnancies. Younger sisters can be identified easily, at the first prenatal visit of the older sister. Because of the unique advantages of identifying these sibs at the point of their highest risk, and also at a time when the family is already receiving services, this discovery could lead to effective programs to prevent multiple pregnancies in the family.